An abbreviation for the programming framework Ruby on Rails (also called "Rails"). This web framework allows developers to build web applications very quickly.
It uses the Ruby programming language, and is known for its speed in prototyping ideas. So, it's a common thing for startups to turn to (at least at this time, ~2010).

A notable feature is that it has generators in the command line that seem "magical" in that they generate a lot of code for the programmer.

"What's the technology stack for your company?"
"We plan to use RoR at first."